Method for preparing an emulsion with high-viscosity organic phase

ABSTRACT

The invention concerns a method for preparing an oil-in-water emulsion whereof the organic phase has a viscosity not less than 1 Pa.s, which consists in using an aqueous phase comprising at least a heat-thickening polymer having a viscosity jump between 25 and 80° C. so that the value of the ratio log  10  (viscosity at 80° C.)/log  10  (viscosity at 25° C.) is at least equal to 1, preferably at least equal to 2, the variation in viscosity being reversible; the amount of heat-thickening polymer being such that the aqueous phase viscosity is 0.2 to 5 times that of the organic phase at the temperature for preparing the emulsion; the latter being not less than the thickening temperature of the heat-thickening polymer.

[0001] The present invention relates to a process for preparing anemulsion whose organic phase is of high viscosity.

[0002] Difficulties are encountered in preparing emulsions with arelatively small droplet size, and obtained from an aqueous continuousphase and an organic discontinuous phase of high viscosity, i.e. with aviscosity at least equal to 1 Pa.s and preferably at least 5 Pa.s.Specifically, the difference in viscosity between the continuous anddiscontinuous phases is such that it is necessary to use high-shearand/or low-efficiency means. In addition, the results achieved are onlypartially satisfactory.

[0003] Solutions have been proposed for obtaining oil-in-water emulsionsvia standard means. These emulsions are obtained in particular by usinglarge amounts of surfactants. Thus, the process is performed startingwith a concentrated aqueous solution of surfactant, as base stock, towhich is added the organic phase. The emulsion obtained may then bediluted.

[0004] The drawback of this process is that it requires the use ofspecially designed equipment. Furthermore, this type of process cannotbe carried out continuously.

[0005] In addition, it is not possible to prepare multiple emulsions(water-in-oil-in-water) using the process described above. The reasonfor this is that as soon as the inverse emulsion (water-in-oil) isintroduced into the concentrated aqueous phase of surfactants, theinverse emulsion is destabilized and only a simple emulsion(oil-in-water) may be obtained.

[0006] The object of the present invention is to obtain a simple andefficient process for preparing an oil-in-water emulsion from a viscousorganic phase, i.e., firstly, requiring the use of only standard means,and, secondly, making it possible to obtain a fine and uniform particlesize for the emulsion.

[0007] Furthermore, the present invention is most particularly suitablefor obtaining multiple emulsions.

[0008] Thus, one subject of the present invention is a process forpreparing an oil-in-water emulsion, the organic phase of which has aviscosity of greater than or equal to 1 Pa.s, in which an aqueous phaseis used comprising at least one heat-induced thickening polymerdisplaying a jump in viscosity between 25 and 80° C. such that the valueof the ratio log₁₀ (viscosity at 80° C.)/log₁₀ (viscosity at 25° C.) isat least equal to 1 and preferably at least equal to 2, the variation inviscosity being reversible; the amount of heat-induced thickeningpolymer being such that the viscosity of the aqueous phase is from 0.2to 5 times that of the organic phase at the emulsion preparationtemperature; said temperature being greater than or equal to thethickening temperature of the heat-induced thickening polymer.

[0009] However, other characteristics and advantages of the presentinvention will emerge more clearly on reading the description and theexample that follow.

[0010] Firstly, it should be noted that the process according to theinvention may be carried out to obtain simple oil-in-water emulsions,but also for multiple emulsions for which the organic phase is in factan inverse emulsion (i.e. water-in-oil emulsion).

[0011] It is pointed out that the mean droplet size of a simple emulsionobtained according to the invention is more particularly between 0.1 and50 μm and preferably between 0.1 and 5 μm.

[0012] In the case of multiple emulsions obtained according to theinvention, the mean size of the droplets dispersed in the externalaqueous phase is between 5 and 100 μm, more partichularly between 5 and50 μm and advantageously between 5 and 15 μm.

[0013] The mean droplet sizes are measured using a Horiba granulometer,and correspond to the median volume diameter (d50) which represents thediameter of the particle equal to 50% of the cumulative distribution.

[0014] In the text hereinbelow, the term “emulsion” is used either todenote a simple direct emulsion (oil-in-water), an inverse emulsion(water-in-oil) or a multiple emulsion, unless the nature of the emulsionis specifically indicated.

[0015] In the text hereinbelow, reference will be made to the “internalaqueous phase” to denote the aqueous phase of the inverse emulsion ofthe multiple emulsion. The term “aqueous phase” will denote either theaqueous phase of a simple direct emulsion, or the “external” aqueousphase of a multiple emulsion.

[0016] Moreover, the term “polymers” denotes both homopolymers andcopolymers.

[0017] The organic phase will now be described.

[0018] Firstly, the compound used as organic phase is chosen moreparticularly from compounds whose solubility in water does not exceed10% by weight at 25° C.

[0019] In addition, as has been indicated previously, the organic phasehas a viscosity of at least 1 Pa.s and preferably of at least 5 Pa.s.The process according to the invention is most particularly suitable forpreparing emulsions for which the organic phase has a viscosity ofbetween 5 and 500 Pa.s.

[0020] It should be noted that the viscosity refers to the dynamicviscosity, measured at 25° C. using a Brookfield viscometer according toAFNOR standard NFT 76 102 of February 1972.

[0021] The organic phase is more particularly chosen from mineral oils;alkyd resins (such as, for example, the Coporob 3115 DE resins sold bythe company Novance); polyisocyanates; high molecular weight silicones;these compounds being alone or as a mixture.

[0022] Among the mineral oils that may be mentioned are polybutene oils.For example, the polybutene oils obtained by polymerization of the Cfraction, the isobutene proportion of which is high (Napvis and Hyvisranges from BP), are suitable for use.

[0023] As regards the polyisocyanates, mention may be made especially ofthe compounds having the following formula: A(-NCOblock)_(p), in which Arepresents an organic skeleton containing n free valences, p beingbetween 2 and 7, and NCOblock represents a masked or unmasked isocyanatefunction.

[0024] More particularly, the total number of carbons in said monomer isadvantageously between 10 and 100.

[0025] In addition, the A skeleton may be made up of a heavy polyamine,including anilines, for example with a carbon number at least equal to6, more particularly at least equal to 10, preferably at least equal to15. This amine is converted in a manner that is known per se by reactionwith phosgene. It should be noted that the A skeleton may also be thatof trimers and biurets.

[0026] Among the masking groups that may be chosen are groups containinglabile hydrogen, with a pKa value of not more than 14, more particularlynot more than 10 and preferably not more than 8. It should be notedthat, the higher the pKa value, the more desirable it is for the maskingagent, if present, to be volatile.

[0027] The masking agents are chosen such that the emulsion is stable atits storage temperature.

[0028] Among the chemical functions capable of masking isocyanates,examples that may be mentioned are the following functions:

[0029] alcohols and thiols

[0030] oximes

[0031] hydroxylamines

[0032] acids

[0033] amides and imides

[0034] β-diketones

[0035] pyrazoles.

[0036] The polyisocyanates that are suitable are more particularlychosen from oils and/or gums and/or resins containing (poly)isocyanategroups, the viscosity of which is within ranges indicated previously. Itwould not constitute a departure from the context of the invention touse several compounds of this type, and likewise their combination withat least one solvent (or diluent) for said oil and/or gum and/or resin,provided that the viscosity of the whole is within the range indicated.

[0037] Among the high molecular weight silicones that may be mentioned,for example, are polyorganosiloxane oils and/or gums and/or resins. Itwould not constitute a departure from the context of the presentinvention to use mixtures of polyorganosiloxane oil(s) and/or gum(s)and/or resin(s), provided that the mixtures have a viscosity within theranges indicated previously. Similarly, the invention is suitable foremulsifying mixtures of polyorganosiloxane oil(s) and/or gum(s) and/orresin(s), and optionally of at least one solvent for said oil(s) and/orgum(s) and/or resin(s), and/or optionally of at least one silane and/orof at least one siliceous and/or nonsiliceous filler, provided that themixtures have viscosities within the mentioned range.

[0038] Among the polyorganosiloxane oils and gums that may be used,mention may be made of those consisting of units of formulae

R′_(3-a)R_(a)SiO_(1/2) and R₂SiO

[0039] in which formulae:

[0040] a is an integer from 0 to 3

[0041] the radicals R, which may be identical or different, represent asaturated or unsaturated C₁-C₁₀ aliphatic radical; a C₆-C₁₃ aromaticradical; a polar organic group linked to the silicon via an Si—C orSi—O—C bond; a hydrogen atom;

[0042] the radicals R′, which may be identical or different, representan OH group; a C₁-C₁₀ alkoxy or alkenyloxy radical; a C₆-C₁₃ aryloxyradical; a C₁-C₁₃ acyloxy radical; a C₁-C₈ ketiminoxy radical; a C₁-C₆amino-functional or amido-functional radical, linked to the silicon viaan Si—N bond.

[0043] Preferably, at least 80% of the radicals R of said oils representa methyl group.

[0044] Among the polyorganosiloxane resins that may be used, mention maybe made of those consisting of units of formulae:

[0045] RSiO_(3/2) (unit T) and/or SiO₂ (unit Q) combined with units offormulae:

[0046] R′_(3-a)R_(a)SiO_(1/2) (unit M) and/or R₂SiO (unit D) in whichformulae a, R and R′ have the definition given above.

[0047] These resins are generally of the type MQ, MDQ, TDM, TD, MT, etc.

[0048] When said oils, gums or resins contain reactive and/or polarradicals R, such as H, OH, vinyl, allyl, hexenyl or aminoalkyl,especially, these radicals generally represent not more than 2% of theweight of the oil or gum and not more than 10% of the weight of theresin.

[0049] The viscous polydimethylsiloxane andα,ω-bis-(hydroxy)polydimethylsiloxane oils and the polydimethylsiloxane,polyphenylmethylsiloxane and α,ω-bis-(hydroxy)polydimethylsiloxane gumsare well-known commercially available products.

[0050] The DT polymethylsiloxane viscous resins containing from 1% to 2%by weight of silanol functions are also commercially available products.

[0051] Among the solvents for the silicone oils, gums or resins, whichmay be present in the silicone phase, mention may be made of volatilecyclic organopolysiloxanes (octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, etc.), short-chain polydimethylsiloxaneoils (viscosity of less than 100 mPa.s), hexamethyldisiloxane, ketones(methyl ethyl ketone, etc.), ethers (diethyl ether, etc.), esters(isopropyl myristate, ethyl acetate, etc.), certain chlorinated orchlorofluorinated solvents (methylene chloride, chloroform, etc.), andhighly branched paraffins (white oils based on isoalkanes andcycloalkanes, etc.).

[0052] Various silanes and/or mineral fillers may also be present in thesilicone phase.

[0053] These silanes may especially be synthetic byproducts orcrosslinking agents for said polyorganosiloxane oils, gums or resins.They are generally present in amounts of from about 0 to 10 parts byweight, preferably of from about 0 to 5 parts by weight per 100 parts byweight of polyorganosiloxane oil(s) and/or gum(s) and/or resin when theyare reaction byproducts.

[0054] When the crosslinking-agent function of the hydroxylated oils,gums or resins is desired, they are generally present in amounts fromabout 0.5 to 30 parts by weight, and preferably from about 2 to 8 partsby weight per 100 parts by weight of oil(s) and/or gum(s) and/orresin(s).

[0055] Said silanes may also be an additive for modulating thephysicochemical properties and especially the adhesion properties of thesilicone compositions of various applications obtained from the aqueousemulsions prepared according to the process of the invention. Among thiscategory of silanes that may be mentioned areaminopropyltriethoxysilane, aminopropylmethyldiethoxysilane,glycidoxypropyltrimethoxysilane, etc.

[0056] They are used in amounts that may be up to 200%, generally fromabout 2% to 100%, of the weight of oil(s) and/or gum(s) and/or resin(s).

[0057] Reinforcing or semi-reinforcing siliceous or nonsiliceous fillersmay also be present. Examples that may be mentioned include colloidalsilicas, combustion silica and precipitation silica powders,diatomaceous earths, ground quartz, natural calcium carbonate, hydratedalumina, magnesium hydroxide, carbon black, titanium dioxide, aluminumoxide, vermiculite, zinc oxide, mica, talc, iron oxide, barium sulfate,slaked lime, etc.

[0058] The size of these fillers is generally less than or equal to themean size of the droplets in which they are dispersed. As a guide, themean size of these fillers (d₅₀) is generally from about 0.001 to 50 μmmand preferably from about 0.001 to 10 μm.

[0059] The fillers are generally present in amounts that may be up to300% and preferably from about 3% to 100% of the weight of oil(s) and/orgum(s) and/or resin(s).

[0060] The organic phase may likewise be chosen from epoxy resins,essential oils, mono-, di- and triglycerides, provided that theirviscosity is within the range mentioned previously.

[0061] The organic phase may optionally comprise at least onehydrophobic active material.

[0062] It should be noted that the organic phase itself may constitutethe hydrophobic active material provided that the organic phase has adynamic viscosity within the range mentioned previously.

[0063] In the case where it is different than the organic phase, theactive material is in liquid or nonliquid form, soluble in the organicphase or dissolved in an organic solvent that is miscible with saidorganic phase, or alternatively in the form of a solid dispersed in saidphase.

[0064] More particularly, the active materials are such that theirsolubility in water does not exceed 10% by weight, at 25° C.

[0065] In addition, the active materials preferably have a melting pointof less than or equal to 100° C. and more particularly less than orequal to 80° C.

[0066] As examples of materials that are active in the food sector,mention may be made of mono-, di- and triglycerides, essential oils,flavorings and colorants.

[0067] As examples of materials that are active in cosmetics, mentionmay be made of silicone oils belonging, for example, to the dimethiconefamily; lipophilic vitamins, for instance vitamin A.

[0068] As examples of active materials that are suitable for performingthe invention, in the field of paints, mention may be made of alkydresins, epoxy resins and masked or unmasked isocyanates.

[0069] In the paper sector, examples that may be mentioned includesizing resins and water-repellant resins such as alkylketene dimer (AKD)or alkenylsuccinic anhydride (ASA).

[0070] In the agrochemicals sector, the plant-protection activematerials may be chosen from the family of α-cyano-phenoxybenzylcarboxylates or α-cyano-halophenoxy carboxylates, the family ofN-methylcarbonates comprising aromatic substituents, active materialssuch as Aldrin, Azinphos-methyl, Benfluralin, Bifenthrin, Chlorphoxim,Chlorpyrifos, Fluchloralin, Fluroxypyr, Dichlorvos, Malathion, Molinate,Parathion, Permethrin, Profenofos, Propiconazole, Prothiofos, Pyrifenox,Butachlor, Metolachlor, Chlorimephos, Diazinon, Fluazifop-P-butyl,Heptopargil, Mecarbam, Propargite, Prosulfocarb, Bromophos-ethyl,Carbophenothion or Cyhalothrin.

[0071] In the detergency sector, possible active materials that may bementioned are silicone antifoams.

[0072] It is similarly possible to use active materials such as thoseforming part of the composition of lubricants for working or deformingmaterials. The active material is usually an oil, an oil derivative or afatty acid ester or a fatty acid salt.

[0073] The active material may also be chosen from organic solvents ormixtures of such solvents that are sparingly miscible or immiscible inwater, especially such as those used for cleaning or stripping, such asaromatic petroleum fractions, terpenic compounds, for instance D- orL-limonenes, and also solvents such as Solvesso®. Solvents that are alsosuitable include aliphatic esters, for instance the methyl esters of amixture of acetic acid, succinic acid and glutaric acid (acid mixtureobtained as a byproduct of Nylon synthesis), oils, for instance liquidpetroleum jelly, and chlorinated solvents.

[0074] In the case where the organic phase comprises one or morehydrophobic active materials different than the organic phase, theircontent more particularly represents 1% to 50% by weight of said organicphase.

[0075] According to one variant of the present invention, the organicphase comprises a dispersed internal aqueous phase. More particularly,the organic phase is an inverse emulsion.

[0076] It should be noted that the viscosity of the inverse emulsion,i.e. of the organic phase comprising the internal aqueous phase, itselfalso has a high viscosity. Thus, the viscosity of the inverse emulsionis at least 1 Pa.s, more particularly at least 5 Pa.s and preferablybetween 5 and 500 Pa.s. The viscosities mentioned above are dynamicviscosities measured using a Brookfield viscometer at 25° C., accordingto standard NFT 76 102 of February 1972.

[0077] In such a case, the organic phase of the inverse emulsion ispreferably of the same nature as that of a simple emulsion. Referencemay thus be made at any point to the list given above.

[0078] The internal aqueous phase, if present, and/or the externalaqueous phase of the emulsion may comprise at least one hydrophilicactive material. Preferably, the hydrophilic active material is in theinternal aqueous phase of the emulsion, when it is present.

[0079] It is pointed out that the hydrophobic and hydrophilic activematerials are determined as a function of their mutual compatibility.Similarly, the hydrophilic active material is chosen so as not tointerfere with the organic phase.

[0080] The hydrophilic active material may be in a form that is solublein the aqueous phase; in a form dissolved in a water-miscible solvent,for instance methanol, ethanol, propylene glycol or glycerol, forexample; or in the form of a solid dispersed in said phase.

[0081] As examples of active materials that may be used in the cosmeticsfield, mention may be made of substances that have a cosmetic effect, atherapeutic effect or any other substance that may be used for treatingthe skin and the hair.

[0082] Thus, active materials that may be used include skin and hairconditioners such as, especially, polymers comprising quaternaryammoniums, which may optionally be incorporated in heterocycles(compounds of the quaternium, polyquaternium, etc. type), humectants;fixing (styling) agents more particularly chosen from polymers (homo-,co- or terpolymers, for example acrylamide, acrylamide/sodium acrylate,polystyrene sulfonate, etc.), cationic polymers, polyvinylpyrrolidone,polyvinyl acetate, etc.

[0083] It is similarly possible to use colorants; astringents, which maybe used in deodorants and which are more particularly aluminum orzirconium salts; antibacterial agents; antiinflammatory agents,anesthetics, sunscreens, etc.

[0084] Mention may also be made of α- and β-hydroxy acids, for instancecitric acid, lactic acid, glycolic acid and salicylic acid; dicarboxylicacids, preferably unsaturated and containing 9 to 16 carbon atoms, forinstance azelaic acid; vitamin C and its derivatives, especially theglycosylated and phosphated derivatives; biocides, especially cationicbiocides (especially Glokill PQ and Rhodaquat RP50, sold by RhodiaChimie).

[0085] In the food sector, examples that may be mentioned includedivalent calcium salts (phosphates, chlorides, etc.) used ascrosslinking agent for texturing polymers, for instance alginates andcarrageenans; sodium bicarbonate, inter alia.

[0086] In the field of plant-protection active materials, hydrophilicpesticides or hydrophilic nutrient elements that promote the growth anddevelopment of plants may be used.

[0087] As regards the field of exploitation or construction of oil orgas wells, the present invention may be carried out for hydrophilicactive materials that may be used especially during operations ofcementation, completion, drilling and stimulation of wells (for examplefracturing). As examples of active materials that may be used in thisfield, mention may be made of crosslinking catalysts for cementcompositions such as, for example, lithium salts, for instance thechloride or the acetate. Mention may similarly be made of compounds thatare capable, inter alia, of degrading polysaccharides, such as, forexample, carboxylic acids (especially citric acid), enzymes (especiallycellulases) and oxidizing agents.

[0088] In the field of silicones, examples that may be mentioned includethe calcium salts and potassium hydroxide, which are used ascrosslinking agent.

[0089] In the field of papermaking, mention may be made especially ofcalcium chloride and hydrochloric acid.

[0090] The amount of hydrophilic active material is more particularlybetween 0.1% and 50% by weight relative to the aqueous phase (whether itis internal and/or external) and preferably between 0.1% and 20% byweight relative to the aqueous phase (internal and/or external).

[0091] When an internal aqueous phase is present, the internal aqueousphase/organic phase weight ratio is more particularly between 10/90 and90/10. This weight ratio is preferably between 30/70 and 80/20.

[0092] Still according to this variant, i.e. according to the one inwhich the organic phase is in the form of an inverse emulsion, theinverse emulsion also comprises at least one nonionic surfactant and/orat least one amphiphilic block polymer and/or at least one cationicsurfactant.

[0093] According to a first variant, the inverse emulsion comprises atleast one nonionic surfactant or at least one amphiphilic block polymer,or a blend of the two.

[0094] It should be noted that the Bancroft rule may be applied to thenonionic surfactant and to the amphiphilic block polymer used (2^(ème)Congrès Mondial de l′ Emulsion [2nd World Conference on Emulsions],1997, Bordeaux, France). In other words, the fraction soluble in thecontinuous phase is greater than the fraction soluble in the dispersephase.

[0095] Thus, the surfactant and the polymer are preferably chosen fromthose that satisfy both the conditions below:

[0096] when they are mixed with the internal organic phase, at aconcentration of between 0.1% and 10% by weight of said phase at 25° C.,they are in the form of a solution throughout all or part of theindicated concentration range;

[0097] when they are mixed with the internal aqueous phase, at aconcentration of between 0.1% and 10% by weight of said phase and at 25°C., they are in the form of a dispersion throughout all or some of theindicated concentration range.

[0098] More particularly, the nonionic surfactant is chosen fromcompounds with an HLB (hydrophilic/lipophilic balance) value of lessthan or equal to 8.

[0099] As examples of surfactants that may form part of the compositionof the inverse emulsion, mention may be made of surfactants, alone or asa mixture, chosen from:

[0100] alkoxylated fatty alcohols

[0101] alkoxylated triglycerides

[0102] alkoxylated fatty acids

[0103] optionally alkoxylated sorbitan esters

[0104] alkoxylated fatty amines

[0105] alkoxylated di(1-phenylethyl)phenols

[0106] alkoxylated tri(1-phenylethyl)phenols

[0107] alkoxylated alkylphenols

[0108] the number of alkoxylated (ethoxylated, propoxylated orbutoxylated) units is such that the HLB value is less than or equal to8.

[0109] The alkoxylated fatty alcohols generally contain from 6 to 22carbon atoms, the alkoxylated units being excluded from these numbers.

[0110] The alkoxylated triglycerides may be triglycerides of plant oranimal origin.

[0111] The optionally alkoxylated sorbitan esters are esters of cyclizedsorbitol of fatty acid containing from 10 to 20 carbon atoms, forinstance lauric acid, stearic acid or oleic acid.

[0112] The alkoxylated fatty amines generally contain from 10 to 22carbon atoms, the alkoxylated units being excluded from these numbers.

[0113] The alkoxylated alkylphenols generally contain one or two linearor branched alkyl groups containing 4 to 12 carbon atoms. Examples thatmay especially be mentioned include octyl, nonyl and dodecyl groups.

[0114] As regards the amphiphilic block polymer, it comprises at leasttwo blocks.

[0115] These amphiphilic polymers, which satisfy the Bancroft rule andthe two conditions stated previously, more particularly comprise atleast one hydrophobic block and at least one neutral, anionic orcationic hydrophilic block.

[0116] In the case where the amphiphilic polymer comprises at leastthree blocks, and more particularly three blocks, the polymer ispreferably linear: in addition, the hydrophobic blocks are moreparticularly located at the ends.

[0117] In the case where the polymers comprise more than three blocks,these polymers are preferably in the form of grafted or comb polymers.

[0118] In the text hereinbelow, even though this is an abuse oflanguage, the term “amphiphilic block polymer” will be used either forthe linear block polymers or for the grafted or comb polymers.

[0119] Said amphiphilic polymers may advantageously be obtained by“living” or controlled free-radical polymerization. As nonlimitingexamples of living or controlled polymerization processes, reference maybe made especially to patent applications WO 98/58974 (xanthate), WO97/01478 (dithioesters), WO 99/03894 (nitroxides); WO 99/31144(dithiocarbamates).

[0120] The amphiphilic polymers may also be obtained by cationic oranionic polymerization.

[0121] They may similarly be prepared by using ringopeningpolymerizations (especially anionic or cationic polymerizations), or bychemical modification of the polymer.

[0122] The grafted or comb polymers may also be obtained by “directgrafting” and copolymerization methods.

[0123] Direct grafting consists in polymerizing the chosen monomer(s)via a free-radical route, in the presence of the selected polymer toform the skeleton of the final product. If the monomer/skeleton coupleand the operating conditions are carefully chosen, there may then be atransfer reaction between the growing macroradical and the skeleton.This reaction generates a radical on the skeleton and it is from thisradical that the graft grows. The primary radical derived from theinitiator may also contribute to the transfer reactions.

[0124] As regards copolymerization, this involves in a first stage thegrafting, onto the end of the future pendent segment, of afree-radical-polymerizable function. This grafting may be performed byusual methods of organic chemistry. Next, in a second stage, themacromonomer thus obtained is polymerized with the chosen monomer toform the skeleton, and a “comb” polymer is obtained.

[0125] Among the hydrophobic monomers from which the hydrophobicblock(s) of the amphiphilic polymer may be prepared, mention may be madeespecially of:

[0126] linear, branched, cyclic or aromatic monocarboxylic orpolycarboxylic acid esters, comprising at least one ethylenicunsaturation,

[0127] saturated carboxylic acid esters containing 8 to 30 carbon atoms,optionally bearing a hydroxyl group;

[0128] α,β-ethylenically unsaturated nitrites, vinyl ethers, vinylesters, vinylaromatic monomers, and vinyl or vinylidene halides,

[0129] linear or branched, aromatic or nonaromatic hydrocarbon-basedmonomers, comprising at least one ethylenic unsaturation,

[0130] monomers of cyclic or noncyclic siloxane type, and chlorosilanes;

[0131] propylene oxide or butylene oxide; alone or as mixtures, and alsothe macromonomers derived from such monomers.

[0132] As particular examples of hydrophobic monomers that may beincluded in the preparation of the hydrophobic block(s) of theamphiphilic block polymer, mention may be made of:

[0133] esters of (meth)acrylic acid with an alcohol containing 1 to 12carbon atoms, for instance methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, n-butyl(meth)acrylate, t-butyl(meth)acrylate,isobutyl(meth)acrylate or 2-ethylhexyl acrylate;

[0134] vinyl acetate, vinyl Versatate®, vinyl propionate, vinylchloride, vinylidene chloride, methyl vinyl ether or ethyl vinyl ether;

[0135] vinyl nitriles more particularly including those containing from3 to 12 carbon atoms such as, in particular, acrylonitrile andmethacrylonitrile;

[0136] styrene, α-methylstyrene, vinyltoluene, butadiene andchloroprene; alone or as mixtures, and also macromonomers derived fromsuch monomers.

[0137] The preferred monomers are esters of acrylic acid with linear orbranched C₁-C₄ alcohols, such as methyl, ethyl, propyl or butylacrylate, vinyl esters, for instance vinyl acetate, styrene andα-methylstyrene.

[0138] As regards the nonionic hydrophilic monomers from which theamphiphilic block polymers may be obtained, mention may be made, withoutwishing to be limited thereto, of ethylene oxide, linear, branched,cyclic or aromatic monocarboxylic or polycarboxylic acid amides,comprising at least one ethylenic unsaturation or derivatives, forinstance (meth)acrylamide or N-methylol(meth)acrylamide; hydrophilicesters derived from (meth)acrylic acid, such as, for example,2-hydroxyethyl(meth)acrylate; vinyl esters allowing the production ofpolyvinyl alcohol blocks after hydrolysis, for instance vinyl acetate,vinyl Versatate® or vinyl propionate, alone or in combination, and alsomacromonomers derived from such monomers. It is recalled that the term“macromonomer” denotes a macromolecule bearing one or more polymerizablefunctions.

[0139] However, the preferred hydrophilic monomers are acrylamide andmethacrylamide, alone or as a mixture, or in the form of macromonomers.

[0140] As regards the anionic hydrophilic monomers from which theamphiphilic block polymers may be obtained, mention may be made, forexample, of monomers comprising at least one carboxylic, sulfonic,sulfuric, phosphonic, phosphoric or sulfosuccinic function, or thecorresponding salts.

[0141] It is pointed out that, under the pH conditions for the use ofthe amphiphilic block polymer, the functions of the anionic block(s) ofthe polymer are in an at least partially ionized (dissociated) form.More particularly, at least 10 mol % of the functions of the block(s)are in ionized form.

[0142] The determination of this value does not pose any problem to aperson skilled in the art; it depends especially on the pKa of theionizable functions of the units of the polymer and on the number ofthese functions (i.e. the number of moles of monomer bearing ionizablefunctions used during the preparation of the polymer).

[0143] More particularly, the monomers are chosen from:

[0144] linear, branched, cyclic or aromatic monocarboxylic orpolycarboxylic acids, and N-substituted derivatives of such acids;polycarboxylic acid monoesters, comprising at least one ethylenicunsaturation;

[0145] linear, branched, cyclic or aromatic vinylcarboxylic acids,

[0146] amino acids comprising one or more ethylenic unsaturations;

[0147] alone or as mixtures, precursors thereof, sulfonic or phosphonicderivatives thereof, and also the macromonomers derived from suchmonomers; the monomers or macromonomers possibly being in the form ofsalts.

[0148] Examples of anionic monomers that may be mentioned, withoutwishing to be limited thereto, include:

[0149] acrylic acid, methacrylic acid, fumaric acid, itaconic acid,citraconic acid, maleic acid, acrylamidoglycolic acid,2-propene-1-sulfonic acid, methallylsulfonic acid, styrenesulfonic acid,α-acrylamidomethylpropanesulfonic acid, 2-sulfoethylene methacrylate,sulfopropylacrylic acid, bis-sulfopropylacrylic acid,bis-sulfopropylmethacrylic acid, sulfatoethylmethacrylic acid,hydroxyethylmethacrylic acid phosphate monoester, and also the alkalimetal salts, for instance the sodium or potassium salts, or the ammoniumsalts;

[0150] vinylsulfonic acid, vinylbenzenesulfonic acid, vinylphosphonicacid, vinylidenephosphoric acid and vinylbenzoic acid, and also thealkali metal salts thereof, for instance the sodium or potassium salts,or the ammonium salts thereof;

[0151] N-methacryloylalanine or N-acryloylhydroxyglycine; alone or asmixtures, and also the macromonomers derived from such monomers.

[0152] It would not constitute a departure from the context of thepresent invention to use monomers that are precursors of those whichhave just been mentioned. In other words, these monomers contain unitswhich, once incorporated into the polymer chain, may be converted,especially by means of a chemical treatment such as hydrolysis, toregenerate the abovementioned anionic species. For example, the totallyor partially esterified monomers of the abovementioned monomers may beused in order thereafter to be totally or partially hydrolyzed.

[0153] As cationic hydrophilic monomers from which the amphiphilic blockpolymers may be obtained, mention may be made especially of:

[0154] aminoalkyl(meth)acrylates and aminoalkyl(meth)acrylamides;

[0155] monomers comprising at least one secondary, tertiary orquaternary amine function, or a heterocyclic group containing a nitrogenatom, vinylamine or ethyleneimine;

[0156] diallyldialkylammonium salts; alone or as a mixture, or thecorresponding salts, and also the macromonomers derived from suchmonomers.

[0157] Said monomers may have a counterion chosen from halides such as,for example, chlorine, sulfates, hydrosulfates, alkyl sulfates (forexample containing 1 to 6 carbon atoms), phosphates, citrates, formatesand acetates.

[0158] Examples of cationic monomers that are also suitable include,inter alia, the following monomers:

[0159] dimethylaminoethyl(meth)acrylate,dimethylaminopropyl(meth)acrylate,di-tert-butylaminoethyl(meth)acrylate,dimethylaminomethyl(meth)acrylamide anddimethylaminopropyl(meth)acrylamide;

[0160] ethyleneimine, vinylamine, 2-vinylpyridine or 4-vinylpyridine;

[0161] trimethylarmoniumethyl(meth)acrylate chloride,trimethylammoniumethyl acrylate methyl sulfate,benzyldimethylammoniumethyl(meth)acrylate chloride,4-benzoylbenzyldimethylammoniumethyl acrylate chloride,(meth)acrylamidotrimethylammoniumethyl chloride orvinylbenzyltrimethylammonium chloride;

[0162] diallyldimethylammonium chloride;

[0163] alone or as mixtures, or the corresponding salts thereof, andalso the macromonomers derived from such monomers.

[0164] Preferably, the amphiphilic block polymers have a weight-averagemolar mass of less than or equal to 100 000 g/mol, more particularlybetween 1 000 and 50 000 g/mol and preferably between 1 000 and 20 000g/mol. It is pointed out that the weight-average molar masses indicatedabove are theoretical molar masses, evaluated as a function of therespective amount of monomers introduced during the preparation of saidpolymers.

[0165] Preferably, an amphiphilic block polymer of nonionic type isused.

[0166] As examples of amphiphilic block polymers that are suitable forcarrying out the invention, mention may be made ofpolyhydroxystearate-polyethylene glycol-polyhydroxystearate triblockpolymers (the products of the Arlacel range from ICI are an examplethereof), and polyalkyl polyether grafted polydimethylsiloxane blockpolymers (for instance the products of the Tegopren brand name sold byGoldschmidt).

[0167] According to a second variant, the inverse emulsion comprises atleast one cationic surfactant.

[0168] In the case of this variant, it is indicated that the cationicsurfactant does not satisfy the Bancroft rule mentioned previously.Specifically, the cationic surfactant is soluble in the dispersed phaseand not in the continuous phase of the inverse emulsion.

[0169] Among the suitable cationic surfactants that may especially beused are aliphatic or aromatic fatty amines, aliphatic fatty amides andquaternary ammonium derivatives (Rhodaquat RP50 from Rhodia Chimie).

[0170] Finally, a third variant of the invention consists in combiningthe two possibilities that have just been detailed.

[0171] Irrespective of the variant selected, the total amount ofnonionic surfactant, of amphiphilic block polymer and/or of cationicsurfactant more particularly represents from 0.1% to 10% by weight andpreferably from 2% to 10% by weight relative to the internal aqueousphase.

[0172] In accordance with one particularly advantageous embodiment, inthe case where the organic phase is in the form of an inverse emulsion,the internal aqueous phase may comprise at least one additive chosenfrom salts such as alkali metal or alkaline-earth metal halides (forinstance sodium chloride or potassium chloride), or alkali metal oralkaline-earth metal sulfates (for instance calcium sulfate), ormixtures thereof. The internal aqueous phase may also comprise, asadditive, at least one sugar, for example such as glucose, or at leastone polysaccharide, such as, especially, dextran, or mixtures thereof.

[0173] The concentration of salt in the internal aqueous phase, when asalt is present, is more particularly between 0.05 and 1 mol/l andpreferably 0.1 to 0.4 mol/l.

[0174] The concentration of sugar and/or polysaccharide is such that theosmotic pressure of the internal aqueous phase comprising said sugarand/or polysaccharide corresponds to the osmotic pressure of an internalaqueous phase comprising 0.05 to 1 mol/l of salt.

[0175] According to an important characteristic of the invention, theaqueous phase of the emulsion comprises at least one heat-inducedthickening polymer.

[0176] Heat-induced thickening polymers have the particular feature ofgiving aqueous solutions whose viscosity increases when the temperatureexceeds the thickening temperature of the heat-induced thickeningpolymer; above this temperature, the viscosity of the medium in whichsaid polymer is present increases.

[0177] More particularly, these polymers are soluble in water at roomtemperature, and above the thickening temperature, some of the polymerbecomes hydrophobic (heat-sensitive portion): the polymer thus forms aphysical network at the microscopic level, which is reflected at themacroscopic level by an increase in the viscosity.

[0178] As has been mentioned previously, the heat-induced thickeningpolymers used in the process according to the invention are chosen fromthose with a viscosity jump between 25 and 80° C. such that the value ofthe log₁₀ (viscosity at 80° C.)/log₁₀ (viscosity at 25° C.) ratio is atleast equal to at least 1.

[0179] The ratio is measured under the following conditions:

[0180] The polymer is first dissolved in water (solids content of 4%).

[0181] The rheological profile is then measured in controlled-stressflow mode, by performing a temperature sweep between 20° C. and 80° C.The configuration used is the cone/plate 4 cm/1 degree geometry. Thestress induced in the program is chosen (in manual model such that thegradient at 25° C. is 10 s⁻¹.

[0182] The magnitude selected to characterize the heat-inducedthickening power of the polymer, i.e. the log₁₀ (viscosity at 80°C.)/log₁₀ (viscosity at 25° C.) ratio, represents the jump in viscosity,expressed in decades, from 25 to 80° C. In other words, this magnitudeindicates that the viscosity of the medium at 80° C. is 10^(n) timesgreater than the viscosity of the medium at 25° C.; with n being aninteger between 0 and 5.

[0183] According to one preferred embodiment of the invention, theheat-induced thickening polymer has a jump in viscosity of at least onedecade and preferably of at least two decades.

[0184] Besides this characteristic, the heat-induced thickening polymersare chosen such that the viscosity variation is reversible. In otherwords, the viscosity decreases when the temperature decreases.

[0185] Among the heat-induced thickening polymers that may be used,mention may be made of hydrophobic modified polysaccharides, forinstance carboxymethyl celluloses, methyl celluloses, hydroxyethylcelluloses and hydroxypropyl celluloses.

[0186] In the case of polymers of this type, it may be advantageous touse them in combination with at least one additional surfactant chosenfrom nonionic and anionic surfactants.

[0187] Synthetic polymers, for instance polymers based onN-isopropylacrylamide and polymers based on N,N-dimethylaminoethylmethacrylate, are also suitable for use.

[0188] According to one particular embodiment of the invention, theheat-induced thickening polymers used have a comb structure consistingof a polymer skeleton segment onto which are grafted at least twoidentical or different polymeric side segments, for which either thepolymer skeleton or the polymeric side segments have a lower criticalsolution temperature, LCST, of between 25 and 80° C.

[0189] It should be noted that the term “segments” covers either alinear chain or a branched chain.

[0190] According to a first variant of the invention, it is thepolymeric skeleton segment that has an LCST of between 25 and 80° C.

[0191] According to a second variant of the invention, which ispreferred, it is the polymeric side segments that have an LCST ofbetween 25 and 80° C.

[0192] Finally, according to another variant of the invention, severalpolymers are used, which are arranged together so as to form acrosslinked structure in which the polymer segments thereof having theLCST contain the crosslinking nodes and at least some of the segmentsthereof not having a lower critical solution temperature of between 25and 80° C. establish connections between said nodes.

[0193] According to these variants, the segment not having the requiredLCST, i.e. of between 25 and 80° C., is itself water-soluble at least inthis temperature range, preferably between 10 and 100° C.

[0194] As regards the polymer segment not having an LCST criticaltemperature, it is more preferably a polymer of water-soluble ethylenictype.

[0195] These water-soluble polymers may be derived from thepolymerization of water-soluble ethylenic monomers. These monomers mayin particular be of vinyl, acrylic, styrene or diene type oralternatively of vinyl ester type.

[0196] Examples of vinyl monomers that may be mentioned includevinylsulfonic acid and methallylsulfonic acid, or salts thereof.

[0197] Examples of acrylic monomers that may be mentioned include(meth)acrylic acid, diacids such as fumaric acid and itaconic acid, orsalts thereof, maleic anhydride, acrylamide and its derivatives such asacrylamidomethylpropanesulfonic acid, or salts thereof.

[0198] Examples of styrene monomers that may be mentioned includestyrenesulfonic acid and vinylbenzoic acid, or salts thereof.

[0199] The water-soluble monomers mentioned above may also be combinedor substituted with hydrophobic monomers, the units of which, onceincorporated into the polymer chain, may be converted, especially bymeans of a chemical treatment such as hydrolysis, into water-solubleunits. Examples of these include methyl(meth)acrylate,tert-butyl(meth)acrylate, glycidyl(meth)acrylate and vinyl acetate.

[0200] Finally, organosoluble monomers of any type may also be used andincorporated into the polymer chain in the form of hydrophobic units.Said monomers, which are present in small amounts in the polymersegment, allow the water solubility of the corresponding polymer to becontrolled.

[0201] Needless to say, the various monomers are selected such that thecorresponding polymer segment has a solubility in aqueous medium inaccordance with the invention. This adjustment of the relative amountsof corresponding monomers is within the capability of a person skilledin the art.

[0202] Monomers such as acrylic acid or methacrylic acid, acrylamidesand derivatives thereof, fumaric acid and maleic acid, and sulfonatedmonomers such as 2-acrylamidomethylpropanesulfonic acid and its alkalinesalts, and vinyl sulfonate, are especially preferred according to theinvention.

[0203] More preferably, this type of polymer segment has a molecularweight at least greater than 1 000 g/mol and preferably at least greaterthan 20 000 g/mol (measured by aqueous GPC, calibration: PEO).

[0204] These polymer segments are advantageously derived from thepolymerization of acrylic acid and/or 2-acrylamidomethylpropanesulfonicacid.

[0205] As regards the polymer segments with an LCST of between 25 and80° C., they are derived from polyoxyalkylene polymers.

[0206] According to one preferred embodiment of the invention, thevarious oxyalkylene units present in the polyoxyalkylene polymer containnot more than 6 carbon atoms.

[0207] Preferably, the segments with an LCST consist of oxyethylene (OE)units and/or oxypropylene (OP) units.

[0208] The OE and OP units may be arranged in the polymericheat-sensitive segment in random, block or sequential form. Thepolymeric heat-sensitive segment may have, for example, a starburststructure. It is found to be possible to adjust the critical solutiontemperature especially by means of the length and composition of thesepolymer segments. Preferably, the segments with a critical temperaturein accordance with the invention consist of at least 5 oxyalkyleneunits.

[0209] More preferably, they are corresponding macromonomers.

[0210] For the purposes of the present invention, a macromonomer denotesa macromolecule bearing one or more free-radical-polymerizable ethylenicfunctions.

[0211] The grafting of the polymeric side segments onto a polymericskeleton segment may be performed according to standard techniques thatare familiar to those skilled in the art (for example European PolymerJournal 4, 343 (1968)).

[0212] Among these standard techniques, mention may be made especiallyof the “direct grafting” and copolymerization techniques.

[0213] Direct grafting consists in polymerizing the chosen monomer(s)via a free-radical route, in the presence of the selected monomer toform the skeleton of the final product. If the monomer/skeleton coupleand the operating conditions are carefully chosen, there may then be atransfer reaction between the growing macroradical and the skeleton.This reaction generates a radical on the skeleton and it is from thisradical that the graft grows. The primary radical derived from theinitiator may also contribute to the transfer reactions.

[0214] As regards copolymerization, this involves in a first stage thegrafting, onto the end of the heat-sensitive segment, of afree-radical-polymerizable function. This grafting may be performed byusual methods of organic chemistry. Next, in a second stage, themacromonomer thus obtained is polymerized with the chosen monomer toform the skeleton, and a “comb” polymer is obtained. It is clear to aperson skilled in the art that when polymerization is performed betweena macromonomer and a monomer chosen such that these two species combinetogether strongly by hydrogen bonding, then there is simultaneous directgrafting onto the polymer segment of the macromonomer and incorporationof this macromonomer into the polymer chain by simple polymerization ofits polymerizable end. In this case, the structure obtained issubstantially more branched or even crosslinked than in the previous twocases.

[0215] Preferably, the polymer comprises 0.1 mol % to 50 mol % andpreferably 0.1 mol % to 5.0 mol % of polymer segments with an LCST ofbetween 25 and 80° C.

[0216] The heat-induced thickening polymers that are most particularlysuitable for the invention comprise at least:

[0217] polymer prepared from PEO-PPO-PEO triblocks and from acrylic acid(respective molar percentages: 2.3%, 97.7%), preferably by directgrafting,

[0218] polymer prepared from PEO-PPO-PEO triblock macromonomer and fromacrylic acid (respective molar percentages: 1.6%, 98.4%), preferably bycopolymerization,

[0219] polymer prepared from PEO-PPO-PEO triblock macromonomer and fromacrylic acid (respective molar percentages: 3%, 97%), preferably bycopolymerization, and/or

[0220] polymer prepared from PEO-PPO-PEO triblock macromonomer and fromacrylic acid (respective molar percentages: 2%, 98%), preferably bycopolymerization.

[0221] These polymers have been described especially in French patentapplication FR 2 780 422.

[0222] The content of heat-induced thickening polymer in the aqueousphase is such that the viscosity of the aqueous phase is from 0.2 to 5times that of the organic phase and preferably from 0.5 to 2 times thatof the organic phase at the preparation temperature of the emulsion;this preparation temperature being greater than or equal to thethickening temperature of the heat-induced thickening polymer.

[0223] For indicative purposes, the content of heat-induced thickeningpolymer is more particularly between 0.5% and 5% by weight relative tothe aqueous phase. Preferably, the content of heat-induced thickeningpolymer is between 1% and 3% by weight relative to the aqueous phase.

[0224] The aqueous phase also advantageously comprises:

[0225] at least one nonionic surfactant and/or at least one nonionicamphiphilic polymer optionally combined with at least one anionicsurfactant and/or at least one anionic amphiphilic polymer; the totalcontent of nonionic and anionic surfactant(s)/amphiphilic polymer(s) isbetween 0.5% and 10% by weight and preferably between 1% and 5% byweight relative to the organic phase or to the inverse emulsion, ifpresent; the amount of anionic surfactant and/or anionic amphiphilicpolymer represents 0.5% to 5% by weight and preferably 0.5% to 2% byweight relative to the weight of nonionic surfactant/nonionicamphiphilic polymer; or

[0226] at least one anionic amphiphilic polymer optionally combined withat least one anionic surfactant; the total content of anionicamphiphilic polymer/anionic surfactant is between 0.5% and 10% by weightand preferably between 1% and 5% by weight relative to the organic phaseor to the inverse emulsion, if present.

[0227] As regards the nonionic surfactants, polyalkoxylated nonionicsurfactants are preferably used.

[0228] Advantageously, said nonionic surfactant is chosen from thefollowing surfactants, alone or as a mixture:

[0229] alkoxylated fatty alcohols

[0230] alkoxylated triglycerides

[0231] alkoxylated fatty acids

[0232] alkoxylated sorbitan esters

[0233] alkoxylated fatty amines

[0234] alkoxylated di(1-phenylethyl)phenols

[0235] alkoxylated tri(1-phenylethyl)phenols

[0236] alkoxylated alkylphenols

[0237] the number of alkoxylated, more particularly ethoxylated and/orpropoxylated, units is such that the HLB value is greater than or equalto 10.

[0238] As regards the polyalkoxylated nonionic amphiphilic polymer, thispolymer satisfies the Bancroft rule and the two conditions thereofstated previously, and comprises at least two blocks, one of them beinghydrophilic and the other hydrophobic; at least one of the blockscomprising polyalkoxylated units, more particularly polyethoxylatedand/or polypropoxylated units.

[0239] Everything that has been stated hereinabove in the context of thedescription of the nonionic hydrophilic monomers and the hydrophobicmonomers that may be used to prepare the amphiphilic block polymersforming part of the composition of the inverse emulsion remains validand will not be repeated here.

[0240] For purely indicative purposes, said polymers are obtained bycarrying out ring-opening polymerizations, especially anionicpolymerizations.

[0241] More particularly, said nonionic polyalkoxylated amphiphilicpolymers are chosen from polymers whose weight-average molar mass isless than or equal to 100 000 g/mol (measured by GPC, polyethyleneglycol standard), preferably between 1 000 and 50 000 g/mol andpreferentially between 1 000 and 20 000 g/mol.

[0242] Examples of polymers of this type that may be mentioned interalia include polyethylene glycol/polypropylene glycol/polyethyleneglycol triblock polymers. Such polymers are well known and areespecially sold under the brand names Pluronic (sold by BASF) andArlatone (sold by ICI).

[0243] According to another embodiment, the nonionic amphiphilic polymeris an amphiphilic block polymer obtained by polymerization of at leastone nonionic hydrophilic monomer and of at least one hydrophobicmonomer, the proportion and nature of said monomers being such that theresulting polymer satisfies the conditions stated previously (Bancroftrule—two conditions).

[0244] These amphiphilic polymers furthermore comprise at least onehydrophobic block and at least one neutral (nonionic) hydrophilic block.

[0245] In the case where said polymer comprises at least three blocks,and more particularly three blocks, the polymer is advantageouslylinear. In addition, the hydrophilic blocks are more particularlylocated at the ends.

[0246] In the case where the polymers comprise more than three blocks,these polymers are preferably in the form of grafted or comb polymers.

[0247] The list of the nonionic hydrophilic monomers and the nonionichydrophobic monomers, and also the various preparation methods, cited inthe context of the description of the amphiphilic block polymers, may berepeated in the case of the polymers according to this variant.

[0248] However, the preferred hydrophilic monomers are acrylamide andmethacrylamide, alone or as a mixture, or in the form of macromonomers;the preferred monomers are the esters of acrylic acid with linear orbranched C₁-C₄ alcohols, such as methyl, ethyl, propyl or butylacrylate, vinyl esters, for instance vinyl acetate, styrene andα-methylstyrene.

[0249] Among the suitable anionic surfactants that may be mentioned,inter alia, alone or as mixtures, are:

[0250] alkylester sulfonates, for example of formula R—CH(SO₃M)—COOR′,in which R represents a C₈-C₂₀ and preferably C₁₀-C₁₆ alkyl radical, R′represents a C₁-C₆ and preferably C₁-C₃ alkyl radical and M representsan alkali metal cation (sodium, potassium or lithium), substituted orunsubstituted ammonium (methylammonium, dimethylammonium,trimethylammonium, tetramethylammonium, dimethylpiperidinium, etc.) oran alkanolamine derivative (monoethanolamine, diethanolamine,triethanolamine, etc.). Mention may be made most particularly of methylester sulfonates in which the radical R is C₁₄-C₁₆;alkylbenzenesulfonates, more particularly of C₉-C₂₀, primary orsecondary alkylsulfonates, especially of C₈-C₂₂, alkylglycerolsulfonates, sulfonated polycarboxylic acids, such as, for example, thosedescribed in GB 1 082 179, and paraffin sulfonates;

[0251] alkyl sulfates, for example of formula ROSO₃M, in which Rrepresents a C₁₀-C₂₄ and preferably C₁₂-C₂₀ alkyl or hydroxyalkylradical; M representing a hydrogen atom or a cation of the samedefinition as above, and also the polyalkoxylated (ethoxylated (EO) orpropoxylated (PO), or combinations thereof) derivatives thereof, suchas, for example, sodium dodecyl sulfate;

[0252] alkyl ether sulfates, for example of formula RO(CH₂CH₂O)_(n)SO₃Min which R represents a C₁₀-C₂₄ and preferably C₁₂-C₂₀ alkyl orhydroxyalkyl radical; M representing a hydrogen atom or a cation of thesame definition as above, n generally ranging from 1 to 4, and also thepolyalkoxylated (ethoxylated (EO) or propoxylated (PO), or combinationsthereof) derivatives thereof, such as, for example, lauryl ether sulfatewith n=2;

[0253] alkylamide sulfates, for example of formula RCONHR′OSO₃M in whichR represents a C₂-C₂₂ and preferably C₆-C₂₀ alkyl radical, R′ representsa C₂-C₃ alkyl radical, M representing a hydrogen atom or a cation of thesame definition as above, and also the polyalkoxylated (ethoxylated (EO)or propoxylated (PO), or combinations thereof) derivatives thereof;

[0254] salts of saturated or unsaturated fatty acids such as, forexample, those of C₈-C₂₄ and preferably of C₁₄-C₂₀, N-acylN-alkyltaurates, alkylisethionates, alkylsuccinamates,alkylsulfosuccinates, . sulfosuccinate monoesters or diesters, N-acylsarcosinates and polyethoxycarboxylates; and

[0255] alkyl ester and/or alkyl ether and/or alkylaryl ether phosphates.

[0256] Among the anionic polymers that may be used, mention may be mademost particularly of block polymers, preferably diblock or triblockpolymers, obtained by polymerization of at least one anionic hydrophilicmonomer, optionally of at least one nonionic hydrophilic monomer, and ofat least one hydrophobic monomer.

[0257] In this case also, the choice of monomers and the respectiveproportions thereof are such that the resulting polymer satisfies thetwo conditions stated previously (Bancroft rule).

[0258] The nonionic and anionic hydrophilic monomers and the hydrophobicmonomers, and also the synthetic modes mentioned in the context of thedescription of the amphiphilic polymers forming part of the compositionof emulsions for which the continuous phase is an oil phase, may be usedto obtain the polymers according to this variant. Reference may thus bemade thereto.

[0259] According to one particular embodiment, and still in the case ofthe variant according to which the organic phase is in the form of aninverse emulsion, it may be advantageous to add to the aqueous phase atleast one additive chosen from salts such as alkali metal oralkaline-earth metal halides (for instance sodium chloride or calciumchloride), at least one alkali metal or alkaline-earth metal sulfate(for instance calcium sulfate), at least one sugar (for example glucose)or at least one polysaccharide (especially dextran), or mixturesthereof.

[0260] The addition of this type of additive makes it possible toequilibrate, if necessary, the osmotic pressures of the aqueous phase ofthe emulsion and of the internal aqueous phase (of the inverseemulsion); the salt, sugar and/or polysaccharide concentrations are setin this respect.

[0261] Furthermore, depending on the application for which the emulsionaccording to the invention is intended, or depending on the nature ofthe active material(s) used, it may be desirable to adjust the pH of theexternal aqueous phase by adding a base (sodium hydroxide or potassiumhydroxide) or an acid (hydrochloric acid).

[0262] According to one advantageous variant of the present invention,the aqueous phase of the emulsion may comprise at least one thickeningpolymer. The purpose of this polymer is to avoid creaming and/orsedimentation of the final emulsion.

[0263] For illustrative purposes, thickening polymers extracted fromplants and optionally modified may be used, such as carrageenans,alginates, carboxymethyl celluloses, methyl celluloses, hydroxypropylcelluloses or hydroxyethyl celluloses.

[0264] Similarly, thickening polymers such as polysaccharides of animal,plant or bacterial origin may be used; nonlimiting examples that may bementioned include xanthan gum, guar and derivatives (for example such ashydroxypropyl guar) or polydextroses, or combinations thereof.

[0265] When it is present, the content of thickening polymer is moreparticularly between 0.1% and 2% by weight relative to the aqueous phaseand preferably between 0.1% and 0.5% by weight relative to the aqueousphase. It is pointed out that, in this concentration range, thethickening polymer is soluble in the aqueous phase.

[0266] The organic phase/aqueous phase weight ratio, or the weight ratioof the internal aqueous phase and organic phase combination/aqueousphase, is usually between 10/90 and 90/10 and preferably between 30/70and 80/20.

[0267] The process for preparing the emulsion more particularly consistsin mixing together with stirring:

[0268] the organic phase comprising:

[0269] optionally at least one hydrophobic active material,

[0270] optionally the dispersed internal aqueous phase optionallycomprising at least one hydrophilic active material and optionally atleast one additive; the combination of internal aqueous phase andorganic phase comprising at least one nonionic surfactant and/or atleast one amphiphilic block polymer, and/or at least one cationicsurfactant; and

[0271] the aqueous phase comprising:

[0272] optionally at least one hydrophilic active material,

[0273] at least one polyalkoxylated nonionic surfactant and/or at leastone nonionic amphiphilic polymer and/or at least one anionic surfactantand/or at least one anionic amphiphilic polymer,

[0274] at least one heat-induced thickening polymer,

[0275] optionally at least one additive and optionally at least onethickening polymer;

[0276] the emulsion preparation temperature being greater than or equalto the thickening temperature of the heat-induced thickening polymer.

[0277] It is similarly pointed out that the emulsion preparationtemperature is preferably greater than or equal to the melting point ofthe organic phase.

[0278] Advantageously, the apparatus used for the stirring is entirelystandard in the field. Thus, a frame paddle may be used.

[0279] It should be noted that the stirring is relatively slow, of theorder of 300 to 700 rpm.

[0280] In the case where the organic phase consists of an inverseemulsion, the process consists in first preparing the inverse emulsionand then mixing this emulsion with the aqueous phase.

[0281] The preparations of a simple direct emulsion (oil-in-wateremulsion) or of a multiple emulsion may themselves also be performedaccording to any known method.

[0282] Thus, by way of example of preparation of a simple directemulsion, a first mixture comprising the compound constituting theinternal organic phase and optionally the hydrophobic active material isfirst prepared.

[0283] Secondly, a second mixture comprising the water, the nonionicand/or anionic surfactant and/or amphiphilic polymer, the heat-inducedthickening polymer, optionally the active material and/or the additive(salt, sugar and/or polysaccharide) and/or the thickening polymer isprepared. According to one particular embodiment for preparing a simpledirect emulsion, the aqueous phase does not comprise additive orthickening polymer.

[0284] The preparation of the aqueous phase preferably consists in firstmixing together the water and the active material, if used, followed bythe surfactant and/or the amphiphilic polymer, with stirring. Next, theheat-induced thickening polymer is added.

[0285] This operation generally takes place at a temperature of between25 and 80° C. and preferably between 40 and 70° C. It is not necessaryfor the temperature during the mixing of the various compounds of theaqueous phase to be greater than or equal to the thickening temperatureof the heat-induced thickening polymer.

[0286] The emulsion is then obtained by adding the organic phase to theaqueous phase, with stirring. It is again pointed out that, according toone characteristic of the invention, this operation takes place at atemperature greater than or equal to the thickening temperature of theheat-induced thickening polymer, so as to limit the difference inviscosity between the two phases of the emulsion.

[0287] More particularly, this operation is performed at a temperatureof at least 25° C., more particularly between 25 and 80° C. andpreferably between 40 and 70° C.

[0288] It is possible to carry out a step of refining of the directemulsion.

[0289] The stirring time may be determined without difficulty by aperson skilled in the art and depends on the type of apparatus used. Itis preferably sufficient to obtain a mean droplet size (d50) that iswithin the ranges mentioned previously.

[0290] In the case of a multiple emulsion, one preparation exampleconsists in preparing a first mixture constituting the internal aqueousphase, comprising the water, optionally the hydrophilic active material,the cationic surfactant, if present, and optionally the additive (salt,sugar and/or polysaccharide). A second mixture is also prepared,comprising the compound constituting the internal organic phase,optionally the hydrophobic active material and the nonionic surfactantand/or nonionic amphiphilic block polymer, if present.

[0291] The first mixture is then added to the second mixture, withstirring.

[0292] The preparation of the inverse emulsion is generally performed ata temperature greater than the melting point of the compoundconstituting the internal organic phase. More particularly, thepreparation temperature for the inverse emulsion is between 20 and 80°C. Advantageously, the preparation temperature for the inverse emulsionis in the region of the preparation temperature for the multipleemulsion.

[0293] It is possible to perform a refining step on the inverseemulsion.

[0294] The stirring time may be determined without difficulty by aperson skilled in the art and depends on the type of apparatus used. Itis preferably sufficient to obtain a mean droplet size (d50) that iswithin the ranges mentioned previously.

[0295] The external aqueous phase of the emulsion is then prepared. Thismay especially be performed by mixing together the nonionic and/oranionic surfactant and/or amphiphilic polymer, the heat-inducedthickening polymer, optionally the active material and/or the additiveand/or the thickening polymer and the water. Preferably, the water andthe active material, the additive, if present, the surfactant and/or theamphiphilic polymer are first mixed together, with stirring. Next, theheat-induced thickening polymer and, where appropriate, the thickeningpolymer are added. It is pointed out that, according to one entirelyadvantageous embodiment, the thickening polymer, if used, is added onlyonce the multiple emulsion has been obtained. In this case, it is usedin the form of an aqueous solution. The water content is such that theconcentration ranges of the multiple emulsion are satisfied.

[0296] This operation generally takes place at a temperature of between25 and 80° C. and preferably between 40 and 70° C. It is not necessaryfor the temperature during the mixing of the various compounds of theexternal aqueous phase to be greater than or equal to the thickeningtemperature of the heat-induced thickening polymer.

[0297] The actual preparation of the multiple emulsion is then performedby adding the inverse emulsion to the aqueous phase, which were preparedpreviously.

[0298] This operation takes place at a temperature greater than or equalto the thickening temperature of the heat-induced thickening polymer.

[0299] This operation thus preferably takes place at a temperature of atleast 25° C., more particularly between 25 and 80° C. and preferablybetween 40 and 70° C.

[0300] Once the multiple emulsion is obtained, the mixture may be leftto cool to a temperature below the thickening temperature of theheat-induced thickening polymer.

[0301] The stirring conditions are preferably of the same type as thoseused during the preparation of the inverse emulsion.

[0302] It is pointed out that it would not constitute a departure fromthe context of the present invention to mix together several multipleemulsions, provided that the external aqueous phases of the mixedemulsions are compatible.

[0303] The emulsion according to the invention may be used as aconstituent component in formulations that may be used in many fields,such as cosmetics, food, the field of plant-protection active materials,that of oil or gas well exploitation or construction, that of silicones,or alternatively in the field of papermaking, inter alia.

[0304] A concrete but nonlimiting example of the invention will now bepresented.

EXAMPLE 1. Preparation of the Heat-induced Thickening Polymer

[0305] 1.1 Synthesis of the Heat-sensitive Macromonomer

[0306] The macromonomer is synthesized in bulk, without catalyst, in thefollowing manner:

[0307] Antarox E400 (EO/PO/EO triblock polymer sold by Rhodia Chimie,200 g) and maleic anhydride (6.74 g) are introduced at room temperatureinto a 500 ml two-necked glass reactor equipped with a condenser and amagnetic bar.

[0308] The temperature is then brought to 60° C. (over about 1 hour),with stirring and flushing with nitrogen, and then to 140° C. (overabout 7 hours) and is maintained at this temperature for 18 hours.

[0309] The macromonomer obtained is then dissolved in water andneutralized by adding 5M sodium hydroxide.

[0310] Its solids content is 28.9% (determined with 1 g of macromonomersolution dried in an oven at 105° C. for 1 hour). The pH is 7.

[0311] 1.2 Synthesis of the Heat-induced Thickening Polymer

[0312] The heat-induced thickening polymer is synthesized via afree-radical route in aqueous solution using acrylic acid andmacromonomer obtained above.

[0313] The polymerization is performed at about 45° C.

[0314] The redox couple used is ammonium persulfate (oxidizing agent)and ascorbic acid (reducing agent).

[0315] The proportions of the various reagents are as follows:

[0316] acrylic acid/macromonomer molar ratio: 98/2

[0317] ammonium persulfate: 0.18 mol % relative to the acrylic acid

[0318] ascorbic acid: 0.09 mol % relative to the acrylic acid.

[0319] The mass concentration of reagents is in the region of 16%.

[0320] The process is as follows:

[0321] The ingredients below are introduced into a thermostaticallymaintained jacketed glass SVL reactor (1.5 l), on which is mounted atubular condenser, and which is equipped with a mechanical stirrer(anchor), several inlets and a nitrogen inlet:

[0322] at 25° C.: the macromonomer in aqueous solution (68.21 g) andwater (139.6 g); the temperature is then increased to 45° C.

[0323] at 45° C.: introduction of sodium persulfate (0.0316 g); thistime is noted to.

[0324] From t° to t°+5 hours: continuous introduction of acrylic acid(21.01 g) dissolved in water (5.14 g) and partially neutralized with 5Msodium hydroxide (4.71 g);

[0325] From t° to t°+8 hours: continuous introduction of ascorbic acid(0.013 g) dissolved in water (15 g).

[0326] The reactor is then cooled.

[0327] The polymer obtained has the following characteristics:

[0328] Determination of the Solids Content by Gravimetry (Conditions1.1): 16.47%

[0329] Determination of the Mean Molar Mass by Aqueous GPC: Conditions:

[0330] water+0.5M LiNO₃+0.06M NaN₃ at 1 ml/min

[0331] 3 Shodex SB 806 M columns

[0332] detector: differential refractometer

[0333] This GPC is calibrated with PEO standards; the molar massesobtained are thus relative values.

[0334] The mass-average molar mass is 310 000 g/mol.

[0335] Heat-induced Thickening Power by Rheology:

[0336] The viscosity of aqueous solutions containing the heat-inducedthickening polymer is measured as a function of the temperature.

[0337] The measuring conditions are as follows:

[0338] pH=8, polymer solids content of 4%.

[0339] The jump in viscosity is measured in controlled-stress flow modeby performing a temperature sweep between 20° C. and 80° C. Theconfiguration used is the cone/plate 4 cm/1 degree geometry. The stressinduced in the program is chosen (in manual mode) such that the gradientat 25° C. is 10 s⁻⁵.

[0340] The jump in viscosity between 25 and 80° C., corresponding to theratio log₁₀ (viscosity at 80° C.)/log₁₀ (viscosity at 25° C.), expressedin decades, is 3.

2. Preparation of an Emulsion

[0341] 2.1 Preparation of an Inverse Emulsion

[0342] 68.6 g of Napvis D30 polybutene (sold by BP) and 1.6 g ofTegopren 7006 (polyalkyl polyether grafted polydimethylsiloxane, sold byGoldschmidt) are successively introduced into a 250 ml beaker.

[0343] The mixture is homogenized by stirring with a frame paddle at 250rpm for 10 minutes, the organic phase being placed in a water baththermostatically maintained at 70° C.

[0344] The aqueous phase is then introduced dropwise under the samestirring conditions.

[0345] The amount of aqueous phase is such that the aqueousphase/organic phase weight ratio is 30/70.

[0346] The aqueous phase comprises 5.2 g of lactic acid (0.1M), 26.2 gof sodium chloride (0.1M) and 0.18 g of Phenonip (biocide, sold by NIPALaboratories).

[0347] Once the aqueous phase has been introduced, the emulsion isrefined by stirring with the frame paddle for 10 minutes at 400 rpm, andthen for 15 minutes at 600 rpm.

[0348] 2.2 Preparation of the Multiple Emulsion

[0349] The external aqueous phase is prepared as follows:

[0350] 5 g of the heat-induced thickening polymer solution obtained inpoint 1.2, 20 g of Arlatone F127G at 5% ((EO)x(PO)y(EO)z polymer withverification of the following equation: 82<x+z<90 and 7 PO units permole of polymer, sold by ICI) and 20 g of distilled water are mixedtogether.

[0351] The initial pH is adjusted by adding sodium hydroxide (2M) toreach a pH of 6-7 (measured at 23° C.).

[0352] The resulting external aqueous phase is introduced into a waterbath at 50° C. with stirring using a TT paddle at 250 rpm, until ahomogeneous phase is obtained.

[0353] 0.5 g of Phenonip is then added.

[0354] 46.8 g of the inverse emulsion obtained previously are introducedby cumulative successive additions to the external aqueous phase, at 50°C., with stirring at 500 rpm for 10 minutes for each addition.

[0355] Once the introduction of the inverse emulsion is complete, arefining operation is performed using a TT paddle at 700 rpm for 30minutes.

[0356] The internal aqueous phase/organic phase/external aqueous phaseweight proportion is 16/35/49.

[0357] The mean droplet size is between 5 and 10 μm (Horiba).

1. A process for preparing an oil-in-water emulsion, the organic phaseof which has a viscosity of greater than or equal to 1 Pa.s, in which anaqueous phase is used comprising at least one heat-induced thickeningpolymer displaying a jump-in viscosity between 25 and 80° C. such thatthe value of the ratio log₁₀ (viscosity at 80° C.)/log₁₀ (viscosity at25° C.) is at least equal to 1 and preferably at least equal to 2, thevariation in viscosity being reversible; the amount of heat-inducedthickening polymer being such that the viscosity of the aqueous phase isfrom 0.2 to 5 times that of the organic phase at the emulsionpreparation temperature; said temperature being greater than or equal tothe thickening temperature of the heat-induced thickening polymer. 2.The process as claimed in the preceding claim, characterized in that aheat-induced thickening polymer of comb structure is used, consisting ofa polymer skeleton onto which are grafted at least two identical ordifferent polymeric side segments, and for which either the polymerskeleton or the side segments have a lower critical solution temperatureof between 25 and 80° C.
 3. The process as claimed in either of thepreceding claims, characterized in that a heat-induced thickeningpolymer for which the polymer skeleton of the polymer has a lowercritical solution temperature of between 25 and 80° C. is used.
 4. Theprocess as claimed in either of claims 1 and 2, characterized in that aheat-induced thickening polymer for which the polymeric side segments ofthe polymer have a lower critical solution temperature of between 25 and80° C. is used.
 5. The process as claimed in one of the precedingclaims, characterized in that a polymer is used comprising severalpolymers arranged together so as to form a crosslinked structure inwhich the polymer segments thereof having the lower critical solutiontemperature contain the crosslinking nodes and at least some of thesegments thereof not having a lower critical solution temperature ofbetween 25 and 80° C. establish the connections between said nodes. 6.The process as claimed in one of claims 1 to 3, characterized in that aheat-induced thickening polymer is used, the segments of which nothaving alower critical solution temperature of between 25 and 80° C. arewater-soluble at least in this temperature range.
 7. The process asclaimed in one of the preceding claims, characterized in that aheat-induced thickening polymer is used, the polymer segments of whichnot having a lower critical solution temperature are water-soluble inthe temperature range for preparation of the emulsion.
 8. The process asclaimed in one of the preceding claims, characterized in that aheat-induced thickening polymer is used, the polymer segment of whichnot having a lower critical solution temperature is a polymer ofwater-soluble ethylenic type.
 9. The process as claimed in the precedingclaim, characterized in that a heat-induced thickening polymer derivedfrom the polymerization of water-soluble ethylenic monomers of vinyl,acrylic, styrene or diene type and/or of vinyl ester type is used. 10.The process as claimed in one of the preceding claims, characterized inthat a heat-induced thickening polymer whose polymer segments have amolecular weight at least greater than 1 000 g/mol is used.
 11. Theprocess as claimed in one of the preceding claims, characterized in thata heat-induced thickening polymer whose polymer segments are derivedfrom the polymerization of acrylic acid and/or2-acrylamidomethylpropanesulfonic acid is used.
 12. The process asclaimed in one of the preceding claims, characterized in that aheat-induced thickening polymer the polymer segments of which having alower critical solution temperature of between 25 and 80° C. are derivedfrom polyalkoxylated polymers is used.
 13. The process as claimed in thepreceding claim, characterized in that a heat-induced thickening polymerwhose polymer segments contain at least 5 oxyalkylenated units is used.14. The process as claimed in any one of the preceding claims,characterized in that a heat-induced thickening polymer chosen from thefollowing is used: polymer prepared from PEO-PPO-PEO triblocks and fromacrylic acid (respective molar percentages: 2.3%, 97.7%), preferably bydirect grafting, polymer prepared from PEO-PPO-PEO triblockmacro-monomer and from acrylic acid (respective molar percentages: 1.6%,98.4%), preferably by copolymerization, polymer prepared fromPEO-PPO-PEO triblock macro-monomer and from acrylic acid (respectivemolar percentages: 3%, 97%), preferably by copolymerization, and/orpolymer prepared from PEO-PPO-PEO triblock macro-monomer and fromacrylic acid (respective molar percentages: 2%, 98%), preferably bycopolymerization.
 15. The process as claimed in any one of the precedingclaims, characterized in that an amount of heat-induced thickeningpolymer is used such that the viscosity of the aqueous phase is from 0.5to 2 times that of the organic phase, at the preparation temperature ofsaid emulsion.
 16. The process as claimed in one of the precedingclaims, characterized in that a content of heat-induced thickeningpolymer of between 0.5% and 5% by weight of the aqueous phase andpreferably between 1% and 3% by weight of the aqueous phase is used. 17.The process as claimed in one of the preceding claims, characterized inthat an organic phase with a viscosity of at least 5 Pa.s and preferablybetween 5 and 500 Pa.s is used.
 18. The process as claimed in one of thepreceding claims, characterized in that an organic phase chosen frommineral oils, alkyd resins, polyisocyanates and high molecular weightsilicones is used; these compounds being alone or as a mixture.
 19. Theprocess as claimed in one of the preceding claims, characterized in thatan organic phase comprising at least one hydrophobic active material isused.
 20. The process as claimed in one of the preceding claims,characterized in that an organic phase comprising a dispersed internalaqueous phase is used.
 21. The process as claimed in claim 20,characterized in that an internal aqueous phase comprising at least onehydrophilic active material is used.
 22. The process as claimed ineither of claims 20 and 21, characterized in that an internal aqueousphase/organic phase weight ratio of between 10/90 and 90/10 andpreferably between 30/70 and 80/20 is used.
 23. The process as claimedin one of the preceding claims, characterized in that the organicphase/aqueous phase weight ratio, or the weight ratio of the internalaqueous phase and organic phase combination/aqueous phase, is between10/90 and 90/10 and preferably between 30/70 and 80/20.
 24. The processas claimed in one of the preceding claims, characterized in that thefollowing are mixed with stirring: the organic phase comprising:optionally at least one hydrophobic active material, optionally thedispersed internal aqueous phase optionally comprising at least onehydrophilic active material and optionally at least one additive; thecombination of internal aqueous phase and organic phase comprising atleast one nonionic surfactant and/or at least one amphiphilic blockpolymer, and/or at least one cationic surfactant; and the aqueous phasecomprising: optionally at least one hydrophilic active material, atleast one polyalkoxylated nonionic surfactant and/or at least onenonionic amphiphilic polymer and/or at least one anionic surfactantand/or at least one anionic amphiphilic polymer, at least oneheat-induced thickening polymer, optionally at least one additive andoptionally at least one thickening polymer; the emulsion preparationtemperature being greater than or equal to the thickening temperature ofthe heat-induced thickening polymer.